When an electronic device operates, internal electronic elements thereof will produce a large amount of heat. Thus, an additional heat dissipating unit is required to enhance heat dissipation of the electronic device, lest the electronic device should have lowered working efficiency or become damaged due to overheating. The heat dissipating unit is usually a radiating fin assembly or a heat sink. However, the heat dissipation effect of the heat dissipating unit alone is limited. Normally, at least one cooling fan is further assembled to the heat dissipating unit, so that the cooling fan produces cooling airflow toward the heat dissipating unit to forcedly carry away the heat transferred to the heat dissipating unit and thereby upgrade the overall heat dissipation performance of the electronic device.
FIG. 1 is an assembled perspective view of a conventional thermal module including a heat dissipating unit 1, which is usually a heat sink or a radiating fin assembly, and a cooling fan 2 fitted to a whole top of the heat dissipating unit 1 via a cooling fan rack 21 to produce and guide cooling airflow to the heat dissipating unit 1 to forcedly carry heat therefrom. FIG. 1A is a top view of the conventional heat dissipating unit 1 with the cooling fan rack 21 connected thereto. Since the cooling fan 2 usually has a fixed size, the heat dissipating unit 1 and the cooling fan rack 21 are usually designed to match the size of the cooling fan 2. This is of course inconvenient to do so. Moreover, the heat dissipating unit 1 includes a plurality of upright and parallelly spaced radiating fins, so that a cooling air passage is formed between any two adjacent radiating fins. The cooling air passages allow the cooling airflow produced by the cooling fan 2 to flow only in a horizontal direction. More specifically, the cooling airflow is directly vertically blown into the air passages among the radiating fins and then flows horizontally toward two lateral sides of the heat dissipating unit 1. Due to the parallel arrangement of the radiating fins, the cooling airflow is stopped from flowing toward two opposite outer ends of the heat dissipating unit 1. As a result, heat is accumulated at a central portion of the heat dissipating unit 1 without being quickly carried away therefrom. The accumulated heat largely lowers the heat dissipation effect. Moreover, due to a blade hub thereof, the conventional cooling fan 2 usually has relatively small airflow near a central portion thereof and relatively large airflow near an outer periphery thereof.
In brief, the thermal module with the conventional cooling fan 2 and heat dissipating unit 1 has the following disadvantages: (1) being subject to accumulation of heat; (2) having low heat dissipation effect; and (3) requiring higher manufacturing cost.
It is therefore tried by the inventor to develop an improved cooling fan rack to eliminate the above disadvantages.